1. Field of the Invention
The present invention relates to an inkjet ink suitably used for image recording by an inkjet method, and an ink cartridge, inkjet recording method, inkjet recording apparatus and ink record using the inkjet ink.
2. Description of the Related Art
Inkjet recording has advantages over other recording methods in that it facilitates full-colorization because of the process that is simpler than those of other recording methods and in that high-resolution images can be obtained even with a simply configured apparatus.
Recently, demands for image quality, color phase, color saturation, glossiness, and durability (scratch resistance, marker resistance and the like) become more exacting in association with technical improvement in OA printers for speed-up and higher image quality.
In order to accomplish high image quality using a regular paper, it is effective to decrease the surface tension of an ink and to increase wettability to the regular paper so as to increase color developing property. Furthermore, a water insoluble resin can be effectively added to an ink to improve image durability.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2003-226827 discloses an ink containing polymer fine particles, a water insoluble or poorly-water soluble colorant, a water-soluble organic solvent and a fluorine surfactant. However, such an ink having a lower surface tension and containing a fluorine surfactant has a problem in that a nozzle plate is easily wet and discharge stability is hard to be ensured.
Additionally, JP-A No. 2004-10733 discloses an ink containing a water soluble solvent, a colorant, water and a polymer which contains at least an alkylene oxide moiety, aromatic ring moiety and carboxyl moiety in one molecule. JP-A No. 2004-10733 also discloses “liquid repellent treatment around a discharge port” and “an ink containing a silicone surfactant, a fluorine surfactant and the like”. However, JP-A No. 2004-10733 does not disclose kinds of silicone surfactants, and the ink having a lower surface tension and containing a fluorine surfactant proposed in JP-A No. 2004-10733 is hard to ensure ink repellency.
JP-A 2007-154021 discloses aqueous dispersions for inkjet recording, which contains a self-dispersible pigment, polymer particles and a compound containing polysiloxane skeleton, and an aqueous ink containing the aqueous dispersions. However, the ink has a surface tension of 25 mN/m to 50 mN/m, which is not intended to obtain an ink having a lower surface tension, and a nozzle plate is not particularly treated.
Therefore, the inventors of the present invention proposed adding a silicone resin in an ink repellent layer of a nozzle plate in an inkjet nozzle so as to decrease a surface tension of an inkjet ink and increase wettability to a recording medium, thereby increasing color development property (JP-A No. 2005-138383). According to JP-A No. 2005-138383, the color developing property of ink can be improved, but ink is needed to be excellent not only in initial ink repellency but also in mechanical durability such as resistant to wiping because of speed-up and increase of frequency of usage of printers. When a conventional inkjet ink is used, initial ink repellency can be ensured, but a dried ink fixes to an ink repellent layer upon continuous printing, causing poor ink repellency.
JP-A No. 2008-95089 discloses an ink containing water, a water soluble organic solvent, a water dispersible resin, a pigment and any one of a fluorine surfactant and silicone surfactant as a surfactant, but fails to mention ink fixation to an ink repellent layer. Practically, the problem of the ink fixation to the ink repellent layer is not solved by the proposed formulation.